(a) A person commits an offense who intentionally or knowingly possesses, manufactures, transports, repairs or sells:

     (1) An explosive or an explosive weapon;

     (2) A device principally designed, made or adapted for delivering or shooting an explosive weapon;

     (3) A machine gun;

     (4) A short-barrel rifle or shotgun;

     (5) A firearm silencer;

     (6) Hoax device;

     (7) A switchblade knife or knuckles; or

     (8) Any other implement for infliction of serious bodily injury or death that has no common lawful purpose.

(b) It is a defense to prosecution under this section that the person's conduct:

     (1) Was incident to the performance of official duty and pursuant to military regulations in the army, navy, air force, coast guard or marine service of the United States or the Tennessee national guard, or was incident to the performance of official duty in a governmental law enforcement agency or a penal institution;

     (2) Was incident to engaging in a lawful commercial or business transaction with an organization identified in subdivision (b)(1);

     (3) Was incident to using an explosive or an explosive weapon in a manner reasonably related to a lawful industrial or commercial enterprise;

     (4) Was incident to using the weapon in a manner reasonably related to a lawful dramatic performance or scientific research;

     (5) Was incident to displaying the weapon in a public museum or exhibition;

     (6) Was licensed by the state of Tennessee as a manufacturer, importer or dealer in weapons; provided, that the manufacture, import, purchase, possession, sale or disposition of weapons is authorized and incident to carrying on the business for which licensed and is for scientific or research purposes or sale or disposition to an organization designated in subdivision (b)(1);

     (7) Involved acquisition or possession of a sawed-off shotgun, sawed-off rifle, machine gun or firearm silencer that is validly registered to the person under federal law in the National Firearms Registration and Transfer Records. A person who acquires or possesses a firearm registered as required by this subdivision (b)(7) shall retain proof of registration; or

     (8) Involved the manufacture and sale of an automatic knife; provided, that the sale of such knife was limited to:

          (A) Retail establishments that represent in writing under oath before a notary public that they only sell the knives to law enforcement officers, military personnel and emergency medical technicians;

          (B) Law enforcement officers;

          (C) Military personnel; or

          (D) Emergency medical technicians. (c) It is an affirmative defense to prosecution under this section that the person must prove by a preponderance of the evidence that:

     (1) The person's conduct was relative to dealing with the weapon solely as a curio, ornament or keepsake, and if the weapon is a type described in subdivisions (a)(1)-(5), that it was in a nonfunctioning condition and could not readily be made operable; or

     (2) The possession was brief and occurred as a consequence of having found the weapon or taken it from an aggressor.

(d) (1) An offense under subdivision (a)(1) is a Class B felony.

     (2) An offense under subdivisions (a)(2)-(5) is a Class E felony.

     (3) An offense under subdivision (a)(6) is a Class C felony.

     (4) An offense under subdivisions (a)(7)-(8) is a Class A misdemeanor.